A multiphase lattice Boltzmann study of droplet evaporation with a pinned contact line

Abstract

Droplet evaporation is a ubiquitous phenomenon in nature and important in numerous practical applications such as spray cooling, inkjet printing, coating, nanoassembly, and nanopatterning. Although the phenomenon seems simple, it is quite complex to model the mass and momentum transport at the solid-liquid-gas contact line and the liquid-gas interface of the droplet. A lattice Boltzmann method (LBM) has become a powerful tool to simulate these complex multiphase flows due to its kinetic nature. In the present study, we investigate the validity of LB simulations to explore the evaporation of a droplet with a pinned contact line in an isothermal system, where the evaporation is dominated by the density gradient of fluid surrounding the droplet. We use a pseudo potential multicomponent LBM to simulate the droplet evaporation. First, we validate our simulation results by comparing the contact angle evolutions of the LB simulation and the analytic solution. Then, we investigate the evaporation-induced velocity inside the evaporating droplet, which has not been studied yet with LBM. For conventional multiphase LB simulations, a meaningful velocity field is rarely obtained due to the presence of the spurious current caused by imbalance between discretized pressures near the interface. By reducing spurious current, the evaporation-induced velocity can be clearly observed. Finally, we compare our simulation results with the analytic solution for time-dependent flow field in an evaporating droplet.